Various nucleic acid species are capable of modifying gene expression. These species include antisense RNA, siRNA, microRNA, RNA and DNA aptamers, anatgomirs, and decoy RNAs. Each of these nucleic acid species can inhibit target nucleic acid activity, including gene expression.
MicroRNAs (miRNAs, miR5) are 20-23 nucleotides (nt) RNA molecules that are produced by the processing of a larger enclosing stem-loop structure (>50 bp), called precursors, by cellular enzymes. miRNAs are processed from hairpin precursors of 70 nt (pre-miRNA) which are derived from primary transcripts (pri-miRNA) through sequential cleavage by the RNAse III enzymes drosha and dicer. miRNAs target the messenger RNA of other genes by binding to their 3′ UTR and interfering with their translation or causing degradation by enzyme targeting double-stranded RNA. miRNAs are non-coding RNAs (ncRNAs) that exist in a variety of organisms, including mammals, and are conserved in evolution. Many miRNAs tend to be clustered and transcribed as polycistrons and often have similar spatial temporal expression patterns. miRNAs have been implicated in various biological processes including developmental timing, differentiation, apoptosis, cell proliferation, organ development, and metabolism